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MARINE TECHNICIAN TODAY
|
FALL 2014
The ECM takes this information from
the MAP sensor and increases the injector
pulse width (the injector stays open longer), therefore
increasing the amount of fuel delivered to the engine. When the
throttle is pulled back, the opposite happens. The ECM controls fuel
management, ignition timing and onboard diagnostics. It continuously
monitors and adjusts these systems. Other sensors such as IAT (intake
air temperature), ECT (engine coolant temperature), and others refine the
fuel delivery of the injector. The ECM has a diagnostic feature that records
engine hours and trouble fault codes.
Having anunderstandingof the basic operationof theMEFI engineswill help
with diagnostic testing, and it will aid in making the correct decisions about
performance upgrades. The high performance segment of the industry has
found that increasing the horsepower on an EFI engine is more difficult
than on an older carbureted engine. On a carbureted engine, changes to
the compression ratio, ignition timing, exhaust, heads, intake manifold,
and camshaft would show and increase in horsepower and torque. The
increased airflow through the engine resulted in more air being pulled and
fuel being delivered through the carburetor. Not so with an EFI engine. The
airflow increases, but not the fuel flow. The fuel flow is still regulated by
the ECM, and it has no way to identify that any modifications have been
made. To gain any performance due to engine modifications will require
changing tuning in the ECM by reprogramming it. There simply is no stock
external means of increasing fuel volume, fuel pressure, or advancing
timing manually. Remember the only way to make more horsepower, no
matter if the engine is carbureted or EFI, is to increase air flow and fuel flow
into the engine in a precise manner. This will keep the stoichiometric ratio
correct throughout the rpm range.
One misconception of EFI engines is that they are self-adjusting. In reality it
is to a point only if the engine is completely stock. The ECM is programmed
for engine size, camshaft type, compression ratio, horsepower output,
idle quality and many more parameters within the engine. Once the base
program is established, compensation parameters for altitude, ambient
temperature, knock and various outputs are programmed into the ECM.
The compensation parameters can only operate within a few percentage
numbers of the base program. If the input signals to the ECM are not within
its programmed parameters, the output for the fuel, spark and timing will
not be correct. It is now easy to see that engine modifications can cause
the engine to run poorly, not stay running, or not start at all. Many times
it will compromise the engine’s fuel economy, reliability and drivability. It
may cause pre-ignition and detonation and ruin a perfectly good engine.
It can take many hours of dynamometer work to develop the proper re-
mapping of the stock ECM.
I have seen boat owners spend thousands of dollars on performance
upgrades to their EFI engine and not gain one ounce of speed. They don’t
have the ability to correctly re-map the ECM and verify proper combustion
.
MEFI 3 ECM
.
FAST Marine EFI install
